Just Installed Pac Brake

[Steve St.Laurent]

I use my exhaust brake ALL the time. I have a switch on my shift lever (5sp) and also have the micro switch on the throttle. Any time I'm downshifting I push in the clutch and rev the engine up to the RPM that it will be in the next gear down before letting the clutch back out. I did this before the exhaust brake and still do it. It's a LOT easier on the syncro's in your transmission not to mention other driveline parts if you match engine speed to the gear you are going into (this applies to upshifting as well). Also by revving it up between gears the EB turns off so when I let the clutch out it's not putting any extra stress on the clutch. If I'm using the truck brakes at the same time then I brake with the heel of my right foot and use my toes on the throttle - takes a little getting used to but comes naturally after a bit. I also manually turn off the exhaust brake with the switch when I'm accelerating because I don't like the idea of slamming the barn door on the turbo when it's at 43 psi!



By driving and using the exhaust brake this way I feel that there is little to no increased stress on the drivetrain. As said above there is a LOT less force on the drivetrain when decelerating with the brake on than when accelerating (even with a stock engine).



JMHO

 

[Wheaties]

Steve,



I don't know how good I'll be at heel and toe on the pedals, but I think revving the engine up to the anticpated speed is a very good idea. I'll definitely give that a try.



I gather there is no delay with the microswitch? Because I'm wired into the ECM, I have a 2-3 second delay after I get off the throttle. This is effectively 'shift time' so you can leave the switch on as long as you want... . I can definitely see pluses and minuses here. In this case I can leave the brake on and it won't activate while I shift, slamming the barn door as you say, a plus. The minus is I might loose a second or two braking time by downshifting with my foot on the throttle.



Good input! Thanks!!

Matt

 

[Steve St.Laurent]

Correct - there's no delay with the microswitch and you hit the nail on the head on the pluses and minuses of it! Oh yeah, one thing to add that hasn't been mentioned - make sure you don't use your exhaust brake for the last 2 minutes or so before you are ready to shut down. If you leave it on your turbo will never cool down. If you use it right until you stop you'll have to wait 5 minutes or so for it to cool.

 

[Wheaties]

Interesting point! Now that you mention it, it makes sense. Here's a related question: My driveway is downhill to my parking space next to the apartments. Without using the exhaust brake, if I roll down the hill in 2nd or 3rd and more or less idle to my parking space, the EGT's are cooler than if I coast to my parking space in neutral. I end up waiting longer for it too cool down. Any idea why? I have a theory, but I'd like to see what you think.



Matt

 

[Steve St.Laurent]

Actually, what you would find if you had a post turbo gauge is that your EGT's are the same either way. By decellerating in gear you are cooling the intake side of the turbo more than the exhaust side (don't ask me why or how). The exhaust side retains more heat.



Try this, next time you pull in go down the hill in gear and turn off at your normal temp that you shut down at. Then sit in the truck and watch the pyro - it will rise quite a bit. Then the next time coast down the hill in neutral and shut down at the normal time and then watch the pyro - it won't rise nearly as much. That's why they say that for shutdown you should really be monitoring a post turbo pyro. I've found that if you drive normally and don't decelerate in gear down to a stop or baby the truck the last few miles that pre and post turbo are very close to each other. If however you baby the truck and hardly open the throttle when you need to speed up a bit and decelerate in gear that you will have a large difference in pre and post temperatures. That's why I have a gauge hooked to a pre-turbo pyro and an Isspro turbo temp monitor hooked to a post-turbo pyro on my truck. The turbo temp monitor automatically turns the truck off when post turbo temps get down to 300 degrees after I remove the key.

 

[Wheaties]

Well that blows my theory! I can remember reading about your experiences with pre and post turbo EGT's over a year ago while my truck was on order, I read it with great interest. I always thought the temperature differential was the result of the differences in thermal mass (if I'm using the right word), if the engine and exhaust manifold store more heat than the turbo, it will take more cooling air to bring it down to an equal temperature. Once that airflow stops, it becomes a matter of thermal conductivity and the temperature equalizes. The manifold cools and the turbo warms up.



My theory was that coasting downhill in gear burns less fuel, read lower exhaust gases, and cools the turbo faster. Hmmm, I wonder if this might not still be true? What do you think Steve? A larger volume of cooler air going through the turbo brings the temp down faster than a small volume of warmer air, causing a larger temperature differential. I never thought much about the intake air in the turbo to tell you the truth... .



A slow cooldown would keep temperature differentials to a minimum, and you'd see very little rise post turbo afterwards.



I'd like to go back and review what you said about pre and post temps back when you got the probes installed. It's something to think about.



Matt

 

[Wheaties]

Okay this is what I have,



Driving into the parking lot at work, flat, 1/2 mile from highway: EGT's climb 30 degrees after shutdown



Pulling into package store after work, downhill offramp, followed by flat: EGT's climb 40 degrees after shutdown



Arriving home, uphill to driveway, then downhill: EGT's climb 30 degrees after shutdown.



In all but the last case, the exhaust brake was used as long as it was relevant, kept out of the throttle for last mile or so. Shutdown at 300F



Matt